Have a go at the shortest IQ test

For those who love to feel superior, but are time-poor, the Cognitive Reflection Test, the world's shortest IQ test with just three questions, is for you. It assesses your ability to identify that a simple problem can actually be harder than it first appears. The quicker you do this, the more intelligent you appear to be. Here are the three questions:

1. A bat and a ball cost $1.10 in total. The bat costs $1.00 more than the ball. How much does the ball cost?

2. If it takes five machines five minutes to make five widgets, how long would it take 100 machines to make 100 widgets?

3. In a lake, there is a patch of lily pads. Every day, the patch doubles in size. If it takes 48 days for the patch to cover the entire lake, how long would it take for the patch to cover half of the lake? The correct answers are at the end of the column.

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Cognitive Reflection Test answers

1. The ball would actually cost 5 cents. If the ball costs X, and the bat costs $1 more, then it will be: X+$1. Therefore bat+ball=X + (X+1)=1.10. Thus 2X+1=1.1, and 2X=0.1, sooo X=0.05.

2. It would take 5 minutes to make 100 widgets. Five machines can make five widgets in five minutes; therefore one machine will make one widget in five minutes too. Therefore if we have 100 machines all making widgets, they can make 100 widgets in five minutes.

3. It would take 47 days for the patch to cover half of the lake. If the patch doubles in size each day going forward, it would halve in size going backwards. So on day 47, the lake is half full.

A survey found a third of people got all three wrong, and 83 per cent missed at least one.